Date: Thu, 21 Aug 1997 08:29:01 -0700 (PDT) From: Tom Samplonius <tom@sdf.com> To: Andreas Klemm <andreas@wup.de> Cc: Stephen McKay <syssgm@dtir.qld.gov.au>, freebsd-hardware@freebsd.org Subject: Re: Quiet SCSI disk? Message-ID: <Pine.BSF.3.95q.970821082249.9973D-100000@misery.sdf.com> In-Reply-To: <19970821120226.20829@wup.de>
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On Thu, 21 Aug 1997, Andreas Klemm wrote: > On Thu, Aug 21, 1997 at 07:18:11PM +1000, Stephen McKay wrote: > > On Wednesday, 20th August 1997, Andreas Klemm wrote: > > > > [about the 4GB DCAS 34330W] > > > > >Do you know how many tags it uses (tagged command queuing) ? > > >It was a bit disappointing for me, that the IBM DORS 32160 2.1GB > > >only offers 3 and the the famous QUEUE_FULL condistion ... > > > > I run mine off a Diamond FirePort 40 (uses the 53c875J chip). When I run > > ncrcontrol, it tells me it is using 4 tags. I don't know if I can use > > more. I remember reading somewhere that Stefan thinks 4 is a good number. > > I can't remember his reasoning, or where I read it. :-/ > > AHC driver uses normally 8 tags. > Or 4 if card doesn't have much SCM space. > And reduces the number of opennings to x, if a queue full race > condition occurs, where x = 3 using the IBM DORS... which is nearly > the same as running without tagged queuing ;-) Beware. The ncr driver allocates up to 4 tags per device. The ahc driver has a certain number of tags per channel (and it isn't easy to see how many tags a device is using). This number is determined by the card type. Most have 16 tags per channel (the 2940UW definitely has 16SCBs). This number can be increased via paging the SCBs to system RAM. Adaptec has been cheapening their 2940 line. The original 2940 had 16 SCBs, but newer cards only have 8. I think the only 2940 with 16 SCBs is the 2940UW. Adaptec also made a 3940 with 255 SCBs, but newer 3940s also only have 16. > -- > Wiechers & Partner Datentechnik GmbH phone: +49 2173 3964 161 > Support Unix - Andreas Klemm fax: +49 2173 3964 222 > An der alten Ziegelei 2 mail1: andreas.klemm@wup.de > D-40789 Monheim mail2: andreas@FreeBSD.ORG > > Tom
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